Medulary thyroid carcinoma (also called MTC) is a relatively rare type of cancer that may occur in certain families, affecting particular cells, called C-cells, in the thyroid. This hereditary type of cancer may also be associated with benign tumors of the adrenal and parathyroid glands. Certain diagnostic tests enable the investigator to detect the presence of abnormal cells in the thyroid and adrenal glands at a very early stage. Pentagastrin is the man-made equivalent of gastrin, a normally present gastrointestinal hormone. The pentagastrin test is designed to determine if there are any abnormalities in calcitonin, a hormone made by the thyroid C-cells. Pentagastrin is capable of stimulating the release of calcitonin into the blood. By measuring the calcitonin in the blood after pentagstrin injection, we are able to determine if the amount of calcitonin is abnormal.